Modification of labels in an array

Question

We want to be able to change the text/image on our JLabel array but we can´t understand why it does not work.

import java.awt.*;

class layoutWindow extends JFrame implements ActionListener {`



    String[] classStrings = { "EN1A", "EN2A", "EN3A", "EN1B", "EN2B", "EN3B",
            "ES1A", "ES2A", "ES3A", "ES1B", "ES2B", "ES3B", "H1", "H2", "H3",
            "N1A", "N1B", "N1C", "N1D", "N1E", "N2A", "N2B", "N2C", "N2D",
            "N2E","N3A","N3B","N3C","N3D","S1A","S1B","S2A","S2B","S3A","S3B" };
    String[] FormationStrings = { "3-3-3", "3-3-2", "2-4-2", "4-4", "2-2-2-2","3-4-3" };
    // Create the combo box, select item at index 4.

     JLabel[] deskLabels = new JLabel[96];



    JComboBox classList = new JComboBox(classStrings);
    JComboBox formationList = new JComboBox(FormationStrings);


    JButton seatbButton = new JButton(" randomize");
    JButton backButton = new JButton("back");
    JButton groupButton = new JButton("Make groups");

    JLabel classLabel = new JLabel("choose class");
    JLabel formationLabel = new JLabel("choose formation");

    JPanel layoutPanel = new JPanel(new GridLayout(8, 12, 1,15));
    JPanel top = new JPanel(new GridLayout(1, 2, 15,1));



    public layoutWindow() {
        super("layout Example");
        setExtendedState(JFrame.MAXIMIZED_BOTH);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        setVisible(true);
        Container contentArea = getContentPane();

        top.setVisible(true);
        layoutPanel.setVisible(true);

            int i = 1;
            for (JLabel label : deskLabels) {
                label = new JLabel();
                if ((i % 12) != 100) {
                    label.setText("" + i);
                    layoutPanel.add(label);}
                else {
                    label.setText("  ");
                    layoutPanel.add(label);
                }
                i++;
     }

        top.add(backButton);
        top.add(classLabel);
        top.add(classList);
        top.add(formationLabel);
        top.add(formationList);
        top.add(seatbButton);

        contentArea.add("North", top);
        contentArea.add("Center", layoutPanel);

        setContentPane(contentArea);
        formationList.addActionListener(this);
        classList.addActionListener(this);
        backButton.addActionListener(this);

    }

    @Override
    public void actionPerformed(ActionEvent event) {


        String string = (String) formationList.getSelectedItem();

         if(string == "4-4"){
            deskLabels[5].setText("aasdggnmh");

         }
        }
        }

layouttaskwindow

public class layouttaskwindow {

    public static void main(String[] args) {

        layoutWindow win = new layoutWindow();
    }

}

We don't understand why this does not work. We create all labels from the array using a for loop but when we try to change them it does not work.we have tried to change it in the ActionEvent but we get no response, could someone please explain how this could be solved?

Could you explain what you expect to happen? There are several errors in this code, but it's not clear what problem you are refering to. My first guess is this line: deskLabels[5].setText("aasdggnmh"); I expect this to throw a NPE since you never put anything into deskLabels. — makrom, Apr 26 '16 at 13:10
well what i want to happen is so my labels within the JLabel array to react to commands, right now it doesn´t at all. — david, Apr 26 '16 at 16:53

Cem Philipp Freimoser · Accepted Answer · 2016-04-26T17:26:52.567

1

I also think (like Hackerdarshi said, I did not read the post, but looks good) the problem is caused by the foreach loop. Not sure, but I think Java does not give you the right reference. So to fix it you could try this:

        for (int i = 0; i < deskLabels.length; i++) {
                deskLabels[i] = new JLabel();
                if ((i % 12) != 100) deskLabels[i].setText("" + i);
                else deskLabels[i].setText("  ");
                layoutPanel.add(deskLabels[i]);
     }

And as Berger said another problem is following line: string == "4-4" Without going deep(for more read this): When you use == you would usually compare by value. But Strings are Object so calling == on a object would compare it reference rather than its value. In Java Strings are special. Therefore it depends on how they initialized what == returns. So just use

string.equals("4-4")

if you want to compare the value of a String

edited Apr 26 '16 at 17:26

answered Apr 26 '16 at 13:11

Cem Philipp Freimoser

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5
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Yes. That, combined with the string comparison tip from Berger, would see the app. working as I understand it to need to work (a string changes in the GUI). – Andrew Thompson Apr 26 '16 at 13:12
yeah right, I added it for ompleteness – Cem Philipp Freimoser Apr 26 '16 at 13:31
*"I added it for ompleteness"* ..now you make me want to up-vote the answer (again!). – Andrew Thompson Apr 26 '16 at 13:42
It should always be like that :P – Cem Philipp Freimoser Apr 26 '16 at 13:45
but label is not defined? – david Apr 26 '16 at 16:45
Yeah, sorry forgot his one... you can access either your label over the array (like I did) or via a variable which hold the reference (Jlabel label = new Jlabel don't forget deskLabels [i] = label) – Cem Philipp Freimoser Apr 26 '16 at 17:30
oh nvm, i solved it, thank you guys very much for your help, me and my friends who are trying to make this really appreciate it, thanks once again – david Apr 26 '16 at 17:34
no problem, please either accept any answer or post your own. So anyone who found that on Google knows what worked for you. – Cem Philipp Freimoser Apr 26 '16 at 17:38

Modification of labels in an array

layouttaskwindow

1 Answers1